Toyota's 2004 Prius petrol and electric hybrid is the first second-generation hybrid car and one which is expected to challenge Honda's Insight for the title of the world's most fuel-efficient car.The Prius uses a 50kW electric motor that is more than 50 percent more powerful than the previous model, and with similar performance to many current petrol-engined small cars. The 2004 Prius is the first Toyota vehicle equipped with its next generation drive-train, named "Hybrid Synergy Drive" which offers greater power and fuel economy with extremely low emissions. The Hybrid Synergy Drive integrates all aspects of Prius' hybrid system, from the proper mix of the electric motor and gas engine for optimum performance and efficiency, to the regeneration of electricity via Prius unique braking system. Regenerative braking is a feature of hybrid vehicles that allows the motor to act as a generator when braking.